Many types of fuel systems used with both spark ignition and compression ignition internal combustion engines are configured such that fuel is constantly recirculated in a loop extending to and from the fuel tank and the engine. This recirculation can disadvantageously result in greatly increased fuel temperatures as the engine's heat is transferred to the recirculating fuel.
U.S. Pat. No. 4,989,572 to Giacomazzi et al. discloses a fuel plumbing arrangement intended to mitigate heat buildup in a fuel tank by returning the recirculated fuel to an in-tank reservoir containing the vehicle's fuel pump.
Although some benefit, in terms of lower fuel temperature, is claimed for the system of the '572 patent, the data contained therein show that improvement is generally not striking. In contrast, a system according to the present invention may be operated so as to eliminate any heating of the fuel in the fuel tank due to recirculation of fuel. Nevertheless, if heating is desired so as to avoid waxing on fuel filters during operation at very low ambient temperatures, or for other reasons, a system according to the present invention may be used to control the fraction of the total fuel flow which is returned to the tank. It is an advantage of the present invention that fuel tank temperature may be controlled by allowing some, all, or none of the fuel being returned from the engine to enter the fuel tank.
According to the present invention, a fuel supply system for an internal combustion engine includes a fuel tank, a pump having an inlet for drawing fuel from the tank and an outlet for transferring fuel to the engine. The pump receives fuel via a fuel supply line extending from the tank to the pump inlet. The fuel supply system also includes a fuel return line extending from the engine to the inlet of the pump such that fuel is recirculated from the engine to the pump inlet without passing into the tank. A fuel supply system according to the present invention may also incorporate an air separator positioned in the fuel return line, with the separator comprising means for removing air from the fuel flowing through the return line and means for diverting a fraction of the returned fuel, including the separated air, to the tank. A fuel supply system according to this invention may additionally include a variable flow restrictor positioned in the return line between the air separator and the pump inlet .